(1) Field of the Invention
This invention relates to an improved process for the preparation of 2,2'-bis[4-(1,1,3,3-tetramethylbutyl)phenol]sulfide which is useful as a light stabilizer, polyolefin modifier, lubricating oil additive, and an intermediate for the manufacture thereof.
(2) Description of the Prior Art
Generally, 2,2'-bis(4-substituted phenol)monosulfides are prepared by reaction of a corresponding 4-substituted phenol with sulfur dichloride. However, further sulfidation in the 6-position of the resulting monosulfide proceeds concurrently to form polynuclear by-products. Moreover, sulfur dichloride takes part in the chemical equilibrium represented by the equation EQU 2SCl.sub.2 .revreaction.S.sub.2 Cl.sub.2 +Cl.sub.2 ( 1)
This leads to a more complicated reaction in which disulfides and other polysulfides are formed as by-products. In many cases, therefore, the end product is undesirably obtained in resinous form and in low yield.
Likewise, 2,2'-bis[4-(1,1,3,3-tetramethylbutyl)phenol]sulfide to which this invention is directed is conventionally prepared by reaction of 4-(1,1,3,3-tetramethylbutyl)phenol with sulfur dichloride, and a number of processes based on this principle are well known. One exemplary process comprises the steps of effecting the reaction in carbon tetrachloride at a temperature of 7.degree. C., diluting the reaction mixture with a large amount of petroleum ether, and then isolating the crystals so precipitated (U.S. Pat. No. 2,971,968 (1961); Chemical Abstracts, Vol. 55, 14385 (1961). Another exemplary process, which has more recently been proposed, comprises the steps of effecting the reaction in a hydrocarbon solvent at a temperature of from 50.degree. to 63.degree. C., cooling the reaction mixture, and then isolating the precipitate so formed (German Pat. No. 1,275,067 (1968). However, these processes adopt the conventional idea of dissolving 4-(1,1,3,3-tetramethylbutyl)phenol in a solvent and then reacting it with sulfur dichloride, and the yield of the end product is as low as 40% for the former process and 17-40% for the latter one. Moreover, these processes require an additional step for the crystallization of the end product by diluting or cooling the reaction mixture. For these reasons, these processes cannot be regarded as economical and suitable for industrial purposes.
On the other hand, it is well known that 4-(1,1,3,3-tetramethylbutyl)phenol reacts with sulfur monochloride (S.sub.2 Cl.sub.2) to form the corresponding disulfide. Specifically, a quantitative yield of 2,2'-bis[4-(1,1,3,3-tetramethylbutyl)phenol]disulfide can be obtained by heating both reactants in the toluene solvent (Tr. Mosk. Inst. Neftekim Gaz. Prom., No. 44, P. 105 (1963)).